1. Field of the Invention
This invention is directed to a completion fluid for reducing the drag caused by friction between metal tubulars in a well during completion or drilling operations in the well. More particularly, chemical additives and polymer particles in an oil phase are added to a water-based fluid such that the particles are transported to an oil film on the surface of the tubulars. The materials disclosed also reduce the amount of corrosion on surfaces of tubulars.
2. Description of Related Art
In recent history the oil and gas industry has discovered that drilling horizontally within an oil and gas reservoir can potentially make a much more productive well. The horizontal well allows access to much larger volumes of the oil- and gas-bearing formation. The longer the lateral or horizontal section the more productive the well can be. For this reason, it has become increasingly common to drill horizontally in many oil and gas formations that are being developed today—particularly in the low-permeability shale formations.
Steel casing is placed in the wellbore and, in many wells, the casing is perforated at a selected number of locations along the horizontal section of the wellbore with clusters or sets of perforations. This starts the process of “completing” the well. The number of sets of perforations may vary from two to forty or more. Hydraulic fracturing fluid is then pumped through each set of perforations—one set at a time. It is common to separate flow in the casing to each set of perforations by setting a drillable bridge plug between them. After hydraulic fracturing treatments have been pumped through each set of perforations, the bridge plugs must be drilled from the casing to allow production up the well from the different sets of perforations.
The length of the horizontal section of the well can be limited by the process of drilling bridge plugs from the casing. Drilling of bridge plugs is often performed with a fluid motor and bit on the end of coiled tubing by pumping a water-based fluid down the tubing, through the motor and bit, and back up the annulus inside the casing. Drilling may also be performed by a workover rig with a power swivel to rotate jointed pipe and turn the bit. The friction between the coiled tubing or jointed pipe and the casing in the horizontal section of the well may become equal to the force available to move the coiled tubing or pipe along the horizontal section, at which point further drilling is not possible. The force available to move the pipe is determined by weight of the pipe in the vertical section of the well and, in some cases, by the force that can be applied by pushing on the pipe with a snubbing mechanism at the surface. When jointed pipe is used, the pipe can be rotated along with the bit and the friction resisting movement of the pipe along the wellbore is decreased, but with coiled tubing the lack of pipe rotation causes higher friction resisting movement along the wellbore. But, even with jointed pipe in wells where the wellbore has been drilled with directional changes, causing “doglegs” or a crooked wellbore, the rotation of jointed pipe and movement along the wellbore may be limited. This means that drilling rigs can sometimes drill longer laterals than completion equipment can complete.
In the past, polymer beads have been mixed with fluids and circulated into the well to reduce friction in both drilling and coiled tubing workovers (J. Can. Pet. Tech., Nov. 1996, p. 7). The effectiveness of these beads in coil tubing and workover applications inside the casing has been limited. It is believed that this is a result of no mechanism to cause the beads to be concentrated in the area where they are needed most—at the metal-to-metal contacts. Consequently, a better friction-reducing fluid is required to reduce friction between coiled tubing and casing caused by the metal-to-metal contact in a water-based fluid. (This type of friction reduction is unrelated to the step of adding water-soluble polymers to the water-based fluid to reduce fluid pressure losses during pumping.)